The crowning promise is that of spiritual support and refreshment through' the dull and dreary time of the Captivity, during which Israel dwells as it were in a desert, without water, or shade, or the relief to the eye which is furnished by the greenery of trees and shrubs.
God was able to make of this "wilderness a standing water, and water-springs of the dry ground" (Psalms 107:35), and he promises to do so (Isaiah 41:18). The soul that longs for him, that thirsts after him, feeling that it dwells "in a barren and dry land, where no water is" (Psalms 63:1), shall be relieved and satisfied by a revelation of God's presence, and an outpouring of his grace unusually copious and abundant.
God's grace is shadowed out under the two similitudes of water and verdure, as in Isaiah 35:7, and, to some extent, in Isaiah 30:23-25.